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80 PCB007 MAGAZINE I NOVEMBER 2021 also addressed the disposition of the extent of corrosion. 4552B contains details on how to calibrate and qualify XRF thickness measuring equip- ment. It also describes how to generate "guard bands" for instruments that do not meet statis- tically acceptable repeatability. 4552B added a method to measure the phosphorous content of the EN deposit. e method uses energy dispersive X-ray flores- cence (EDXRF). Here, a number is generated for % phosphorous in the EN deposit. is number is a good indicator of the EN bath per- formance over its life as measured by MTOs (metal turnovers). e number can also be used to establish a correlation between the occurrence of corrosion and the % phospho- rous content of the EN deposit. With this methodology, manufacturers can gain a good understanding of the defect. ey can track it, attempt to define a root cause, and eventually eliminate the defect. Products can be shipped with confidence, knowing that the product will not be rejected for ENIG corrosion. Buyers can request that the manufacturer perform corrosion testing per 4552B and sup- ply support documentation that the product is corrosion-free, or with an acceptable level of corrosion that will not cause solderability issues. Suppliers now have a way to evaluate the performance of products in the field. ey can increase the robustness of their products and service to ensure that customers can produce acceptable ENIG finishes in different manufac- turing environments. Manufacturing sites vary dramatically in level of engineering support, lab support, plater experience, equipment, QC capability, etc. Specific examples of increasing product robustness include: • A modified catalyst that will produce a uniform catalyzed surface • A more corrosion-resistant electroless nickel • A non-aggressive immersion gold • A reduction-assisted immersion gold For technical service, the supplier must have a team of service engineers that are well versed on nickel corrosion and are supported by an analytical lab with capable personnel that can produce product rating numbers and % phos- phorous as specified in 4552B. e revised ENIG Specification 4552B gave the industry a tool by which manufacturers, buyers, CMs, and suppliers can measure the extent of ENIG corrosion. With this measure- ment tool, the problem of ENIG corrosion is well on its way to be eliminated. "You can't fix a problem that you can't mea- sure." PCB007 George Milad is the national accounts manager for tech- nology at Uyemura. To read past columns or contact Milad, click here. Table 2: Revision 4552B assesses the frequency of occurrence or prevalence of the corrosion defect.

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